A cable robot is a parallel kinematics robot in which a platform is positioned and moved in space by means of cables pulling the aforementioned platform. Each cable extends between an attachment point and a winch, whether the winch is attached to the platform and the attachment point attached to a fixed structure, or the winch is attached to a fixed structure and the attachment point is fixed to the platform. In many embodiments, the track followed by the cable between the attachment point and the winch comprises at least one pulley, for reorienting the cable, the position in space of the platform being given by the length and direction of the part of the cables extending between the platform and the proximal pulley. As a convention, in the following, each cable is considered to extend between an attachment point connected to the platform, and an anchoring point connected to the supporting structure. The ability to change the length of the cable strand extending between the attachment point and the anchoring point, makes it possible to cover a large working volume with a light and easily installed supporting structure, for example by setting up the anchoring points on poles or on the ceiling of a workshop. The stability of the platform, in a given position, is given by its static equilibrium, which equilibrium is carried out by the tension of the cables which act so as to counteract the external forces to which the aforementioned platform is subjected.
Document GB 2.495.958 describes such a device. Though such a prior art robot has a large potential workspace, a great part of this workspace is actually limited by so called, collision phenomena, this term being taken in a broad sense.
Thus, part of the workspace is not accessible to certain kinematics, because of an interference or collision risk, between the cables themselves. Moreover, when an item lays in the environment of the robot, there is a collision risk between this item and the cables for certain trajectories. Finally, certain parts of the workspace are accessible with various cables configurations, all of which do not exhibit the same stability of the platform. These collision phenomena are generally known in robotics but their resolution is much more complex in the case of a cable robot because, on the one hand, of the greater covered volume, and specifically, because of need for balancing in intensity and orientation the forces applied by the cables to the platform to ensure its stability, each cable having to act on the platform in a direction corresponding to a tension of the cable, which introduces additional constraints. The stability of a particular posture of the platform, is defined by the capacity of the device to resist any force wench applied to the platform, while each cable remains in a range of permissible elastic deformation.
In the case of a trajectory, the static equilibrium of the platform must be performed in each point making the trajectory, i.e. in a continuous way.
The document “On the Design of Adaptive Cable-Driven Systems”, by Rosati and Al, in Journal of Mechanisms and Robotics, Vol 3, May 2011, describes a method for optimizing the position of the mobile anchoring points of a cable robot, but is limited to the case where the anchoring points are contained and move in a plane, and does not take into account the possible collisions with an item contained in the workspace of the robot. The inventors noted that the method recommended in this document cannot be used for the determination of an optimal configuration for a trajectory, in the case of a device comprising a three-dimensional distribution of the anchoring points. Indeed, the method recommended in this document relies on a variational analytical expression of the static equilibrium conditions, which in the case of a force wrench whose components are three-dimensional is not tractable from the point of view of modeling. In addition, from a practical point of view, the principles described in this document cannot be implemented easily, or even cannot be implemented at all, in the case of a three-dimensional distribution of anchoring points. As a matter of fact, the method recommended in this document, consists in determining a configuration of anchoring points adapted to a given situation and then to move the aforementioned anchoring points according to a mode which preserves this configuration, actually consisting in moving the anchoring points on circles A three-dimensional extrapolation of the teachings of this document would consist in considering the displacement of anchoring points on spheres, this kind of implementation being particularly complex and expensive.